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How Fast is a 50cc Dirt Bike

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The most popular metric for the performance of a motorcycle is its speed, and in this article, we investigate and answer the question; how fast is a 50cc dirt bike?

Whether you’re shopping around for your kids first dirt bike,or simply curious. It’s always interesting to compare the performance of dirt bikes in each bracket to determine the best bang for buck, or at least which is most suitable for your application.

The staple kids dirt bike has been the little 50cc motocross style bike, and it has been for years. 50cc seems to have ended up as the sweet spot for these smaller bikes and can actually give a lot of head-room for young riders as they gain more confidence.

So unlike their shoes, a 50cc dirt bike could be a good fit for them for years, possibly even from age 3 all the way to age 9.

Read on to find out the performance stats and specs of the more common 50cc dirt bikes and a comparison.

How Fast can a 50cc dirt bike go

It’s difficult to generalise and put all 50cc motorcycles in the same bracket, there are a very large number of bikes with this engine size and their state of tune and efficiency can vary considerably.

Your first experience of a small 50cc engine might have been on a moped scooter that topped out at a surprisingly high 50mph, but took forever to build up to that even with a tail wind on a smooth straight road.

The truth is, mopeds are a very different type of motorcycle to a kids dirt bike, and unlike dirt bikes, they are actually designed to cruise at higher speeds to keep up with the flow of traffic, and the way they do this is simple; it’s all about gearing.

If you’re interested in finding out what a 50cc dirt bike top speed is, you may come away somewhat disappointed as most from the factory can deliver around 30-40mph top speeds in ideal circumstances.

The gearing of a dirt bike is much shorter which means the engine can provide more wheel torque in a given gear, and thus harder acceleration, but this shorter final drive ratio also takes away from the bikes top speed.

If you could fit on one, a kids 50cc dirt bike would feel a lot peppier than the aforementioned moped did, and on dirt you would find it surprisingly nimble and capable.

The current market has more variety than yesteryears however, the stalwart kids dirt bikes such as the Yamaha TTR 50 and Honda CRF50 are still everpresent, but there are some newcomers to the kids 50cc dirt bike market which have more emphasis on performance for those more confident child riders.

Here is a rundown of the top 50cc dirt bikes for children and their top speed.

Yamaha TTR 50 Top Speed – 32mph

The Yamaha TTR 50 is the first bike which springs to mind when you think childs dirt bike, and it’s easily the most popular and common on the market.

The TTR 50 is equipped with a 50cc 4-stroke motor similar to those found in pit bikes, and a semi-automatic 3-speed gearbox making it a real pleasure for a kid to jump on and ride.

However, the top speed of the TTR50 is a bit on the low side, and while it should be ample power for all young riders just getting into the sport, it’s more geared up for beginners.

The TTR 50 is possibly the ideal first dirt bike for any kid.

Honda CRF50 Top Speed – 33mph

Interestingly, when it comes to TTR50 vs CRF50, Honda’s 50cc offering comes out marginally on top with an additional 1mph over the Yamaha.

This may be a cheeky trick from the Honda marketing department and an attempt at one upmanship, but nevertheless 33mph is the top speed.

The CRF50 has more or less the same setup too, with that 50cc 4-stroke engine and semi-auto transmission.

As far as real-world performance goes, the Honda is another prime example of a childs dirt bike and you’d be very hard pressed to split between it and the TTR50 in their stock forms. So it might be more a choice of red or blue in this case.

KTM 50 SX Top Speed – 45mph

I previously mentioned newcomers to the kids 50cc dirt bike market, and while it may be a stretch to refer to KTM as new, it’s certainly late to the party compared to Yamaha and Honda.

The KTM 50 SX has proved to be a bit of a performance game changer in the 50cc space, and this bike is a much more focused motocross bike, unlike its Japanese counterparts.

The KTM 50cc engine is a 2-stroke motor offering quite a bit more power for the same displacement, meaning this 50cc dirt bike can go a surprisingly quick 45mph, and can arrive there quicker too.

If your kid is a confident rider and looking to move into the motocross discipline, this will happily be the correct bike for the job, its set up to go, handle and even stop better with its disc brakes.

What’s the Fastest 50cc Dirt Bike?

KTM are not the only manufacturer to notice the opportunity in the 50cc market for more hardcore offerings, companies like Cobra and Husqvarna have followed suit and began to release comparable offerings to the 50SX.

The real key to this is the 2-stroke engine as opposed to the 4-stroke. With a 2-stroke motor, there are considerably more combustion, or power strokes, within a given timeframe. However the tradeoff with this is emissions and potentially engine longevity.

At this moment in time, all of the fastest 50cc dirt bike top speeds are 45mph in stock form, and they are all 2-stroke bikes, so it’s impossible to split them and determine the more powerful bike.

But if 45mph is not enough for you, and you’re looking to modify a bike and increase the top speed of a 50cc dirt bike even further, there are aftermarket options available for you which I will cover in the next section.

How to make a 50cc dirt bike faster

In the world of motorcycles and cars, it’s always tempting to go down the rabbit hole of modification to eek out improved performance. Sometimes it’s worth it, and other times it’s a case of diminishing returns.

When it comes to 50cc dirt bikes however, there are clear areas for improvement over the factory configuration.

To simplify things, there are two opportunities to adjust the performance of these bikes:

  1. Gearing
  2. Engine power output

Addressing point number one first, gearing.

50cc Dirt Bike Gearing

This is one of the most common mistakes we come across when it comes to modifying dirt bikes. This is usually down to an individual’s interpretation of what the word “faster” means.

In the world of dirt bikes, you’re rarely reaching anywhere near the bikes top speed on a track or a trail, nor would it make sense to be trying to. Thanks to this, we’d generally recommend seeking more low down torque and power allowing the motorcycle to accelerate harder instead.

But if you are looking to set some kind of 50cc land speed record, you can adjust in the other direction just as easily.

You can make some significant adjustments to the way power is delivered in this respect with gearing.

Adjusting the final drive ratio of a dirt bike can generally be done by altering the size of the front and/or rear sprockets. This works by changing the amount of revolutions the engine needs to make to turn the rear wheel a given amount. The general rules for this is laid out below:

  • Larger front sprocket: Harder acceleration, lower top speed
  • Smaller front sprocket: Softer acceleration, higher top speed
  • Larger rear sprocket: Softer acceleration, higher top speed
  • Smaller rear sprocket: Harder acceleration, lower top speed

If you’re really serious about top speed, you can combine a smaller front sprocket with a larger rear sprocket to maximise that and potentially see your 50cc dirt bike reach speeds of up to 60mph, albeit accelerating slowly.

50cc Dirt Bike Tuning

The second opportunity I mentioned when it comes to making your 50cc dirt bike faster is engine power output, or in other words, tuning your bike to burn more air and fuel to produce additional power.

As with most stock motorcycles, the performance of certain parts is a compromise. This can often be down to cost, and at other times a tradeoff for reliability.

With 50cc dirt bikes, the bottleneck on performance is often the exhaust. Fitting an aftermarket exhaust which is a higher quality, and more free-flowing unit can unlock a few extra horsepower straight away. It can also make the bike sound faster too.

If you also match this upgraded exhaust with a more free-flowing air filter and then tune the carbs jetting to make most efficient use of this more free-flowing setup you can start to make some tangible power gains.

However, these will be very modest compared to the changes that can be made with gearing, as at the end of the day, we’re still talking about a small 50cc motor.

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